Want to stop algal blooms? Stop feeding the algae

Debbie Akins

5 months ago

The cyanobacterial blooms that have plagued South Florida this summer have led to protests from the public, promises from politicians and blame (mostly targeted at farmers and Lake Okeechobee) from the coastal media.

But amid all of the slogans, sound bites and allegations, maybe we’re asking the wrong question.

Instead of asking where the algae or cyanobacteria (which is not technically algae but is commonly called blue-green algae) is coming from, maybe we should be asking what — or who — is feeding it.

Algae is found naturally in lakes and streams, not just in Florida but all over the world. When freshwater algae has a plentiful source of food (as in nitrogen and phosphorus) combined with hot weather, low salinity and little water movement, it can reproduce rapidly into a bloom.

Humans can’t control the weather and have limited control over water movement. What we could control — although it won’t be easy and it won’t be cheap — is the food supply.

Think about it. If alligators or birds or other potential nuisance animals are hanging around a boat dock, and are making a mess and/or creating a health hazard, the first step is to make sure no one is feeding them. The same goes for algae.

In South Florida this summer, algae has been feasting in waterways throughout the state, not just in Lake Okeechobee. But to focus on the big lake, the summer began with a massive body of water (1 inch on the lake is a staggering 12 billion gallons of water) that was high in phosphorus and nitrogen. According to presentations at U.S. Army Corps of Engineers and South Florida Water Management District meetings, the high levels of dissolved nutrients in the lake in the early summer were thanks to the aftereffects of Hurricane Irma. The hurricane, which hit a year ago next month, churned the lake, stirring up the build-up of muck that had accumulated in the “bowl” of the lake bottom. At one point, the hurricane winds were so strong that water was pushed up 10 feet higher on one end of the lake than the other. When the winds let up, the water sloshed back down. The storm also tore up the lake’s natural vegetation, which is the lake’s filter system.

High lake levels, also courtesy of Hurricane Irma, gave the lake little time to recover, as it dipped below 13 feet for only a short time before record rainfall hit in May.

When the algae bloom started on Lake Okeechobee, most of the tests indicated the dominant species was Microcystis aeruginosa. In July, the bloom grew to include 90 percent of the lake, according to National Oceangraphic and Atmospheric Administration satellite imagery. Then something happened; the bloom started to dissipate. It shrank down to about 10 percent of the lake. At the time, Dr. Karl Havens, director of Florida Sea Grant, theorized that the Microcystis may have consumed all of the available nitrogen and was starving. Some algae can “fix” nitrogen from the air. Microcystis cannot. When the NOAA imagery indicated the algae concentration was increasing again, Dr. Havens theorized that another species of algae — one that could fix nitrogen from the air — was present.

In his blog on flseagrant.org, Dr. Havens wrote “Appearance of Anabaena is consistent with the hypothesis that the bloom is going through a replacement cycle, where Microcystis has used up the nitrogen in the lake water and is being replaced by a different kind of algae that can get its nitrogen from the atmosphere, like Anabaena.”

Dr. Havens’ theory was later proved by testing water samples from the lake. On Aug. 7, Dail Laughinghouse, an assistant professor of applied phycology at the UF/IFAS Fort Lauderdale Research and Education Center, collected water samples from Lake Okeechobee. He found the samples of blue-green algae included three species of Microcystis and six species of Anabaena.

Meanwhile, the Microcystis aeruginosa growing in the coastal waterways showed no signs of running out of nitrogen. In July, when lake releases to the St. Lucie Canal were suspended for nine days, the algae bloom at the St. Lucie Lock continued to grow in intensity, nearly 24 miles from Port Mayaca where the lake water enters that waterway. Even if the Microsystis bloom there was seeded by the lake releases — which is possible but has not been proven, according to Dr. Havens — the algae must have found a local source of food in the St. Lucie Canal.

South Florida Water Management District research has found the phosphorus levels in the St. Lucie Canal to be higher than the phosphorus levels in the lake water.
According to studies by Florida Atlantic University, the nitrogen levels in the St. Lucie Canal are higher than the nitrogen levels in Lake Okeechobee. The study also found the nitrogen levels grow highest closer to the populated coastal area.

“The solution to the algal bloom problem is to clean up the nutrient sources north of Lake Okeechobee and in the land around the two estuaries,” stated Dr. Karl Havens. “Control of dispersed sources of nutrients in those watersheds will be a huge challenge, and while projects are underway by the state to accomplish them, it could take decades before substantive results are seen.”

The Florida Sea Grant publication “Harmful Algae Blooms Affecting Florida Coast,” says the most direct solution is to reduce nutrient inputs to estuaries, the coastal ocean, lakes and rivers before that happens.

Remediation measures include:

• Switching old neighborhoods from septic to central sewage;

• Reducing the use of fertilizer to recommended levels on crops or capturing and cleaning the runoff water from those lands;

• Controlling the export of nutrients in manure from animal agriculture;

• Changes in land use, including in residential neighborhoods, to species of plants that do not require addition of nutrients because they are adapted to grow in our native soil.

“The overall costs are great, because there are places in Florida where past nutrient pollution has left a legacy of nutrients in wetlands, soils and on the bottom of rivers and canals — that all drain into lakes, estuaries and the ocean after heavy rainfall. Controlling that legacy pollution may take massive public works projects to capture water and treat it. Yet, inaction has the potential to allow massive, highly toxic blooms to impair the use of our inland and coastal waters in the future and increase the risks to human health. It is certain that if we wait until the waters are warmer, the costs will be much higher and the outcomes less certain to be successful,” the Florida Sea Grant publication states.